Force sensor and method of manufacturing the same

Abstract

A sensor substrate includes a plurality of piezoresistance elements. The electrical resistance of each piezoresistance element changes in accordance with an amount of displacement of a displacement portion displaced by an external load applied through a pressure receiving unit. A base substrate supports the sensor substrate. The sensor substrate and the base substrate each include a support supporting the displacement portion such that the displacement portion can be displaced and a plurality of electrically connecting portions electrically connected to the plurality of piezoresistance elements. The supports of the sensor and base substrates are joined to each other and the plurality of electrically connecting portions of the sensor and base substrates are joined to each other. Furthermore, in each of the sensor and base substrates, either the support or the plurality of electrically connecting portions or both extend to the periphery of the sensor substrate or the base substrate.

What is claimed is: 
     
       1. A force sensor having a sensor substrate joined to a base substrate,
 wherein the sensor substrate comprises:
 a pressure receiving unit formed on a first surface of the sensor substrate; 
 a displacement portion configured to be displaced by an external load applied thereto through the pressure receiving unit; 
 a plurality of piezoresistance elements provided on a second surface of the sensor substrate opposite to the first surface, each of the plurality of piezoresistance elements having an electrical resistance that changes in accordance with an amount of displacement of the displacement portion; 
 a sensor-side support provided on the second surface of the sensor substrate, configured to displaceably support the displacement portion, the sensor-side support being formed in a shape having an inner peripheral edge enclosing an entire periphery of the displacement portion in plan view, at least part of the sensor-side support overlapping the plurality of piezoresistance elements in plan view; and 
 a plurality of sensor-side electrically connecting portions provided on the second surface along a periphery of the sensor substrate so as to surround an outer periphery of the sensor-side support, each of the plurality of sensor-side electrically connecting portions being electrically connected to a corresponding one of the plurality of piezoresistance elements, and located at a separated position that does not cross a virtual line passing through a center of the pressure receiving unit and a center of each of the plurality of piezoresistance elements, 
 
 wherein the base substrate includes:
 a base-side support provided on a surface facing the sensor substrate, the base-side support being joined to the sensor-side support; 
 a plurality of base-side electrically connecting portions provided on the surface along a periphery of the base substrate so as to surround an outer periphery of the base-side support, the plurality of base-side electrically connecting portions being connected to the plurality of sensor-side electrically connecting portions; and 
 a plurality of electrode pads formed at ends of electrical wiring extending from the base-side electrically connecting portions, the plurality of electrode pads providing electrical connections to external circuitry, 
 
 and wherein the sensor-side support is joined to the base-side support with a metal joint layer disposed therebetween, and each of the plurality of sensor-side electrically connecting portions is joined to a corresponding one of the plurality of base-side electrically connecting portions with a metal joint layer disposed therebetween, each of the metal joint lavers having a thickness of 300 nm or smaller and being formed of an alloy including one or more of materials selected from the group consisting of Al, Ti, Cr, Ni, Cu, Ru, Rh, Ir, Pt, Ta, Fe, and Au, or a multilayer film composed of two or more lavers each including a material selected from the group consisting of Al, Ti, Cr, Ni, Cu, Ru, Rh, Ir, Pt, Ta, Fe, and Au. 
 
     
     
       2. The force sensor according to  claim 1 ,
 wherein the sensor-side support also serves as one of the plurality of sensor-side electrically connecting portions. 
 
     
     
       3. The force sensor according to  claim 1 ,
 wherein the base-side support has a shape having an inner peripheral edge corresponding to the inner peripheral edge of the sensor-side support in plan view, the sensor-side support and the base-side support being joined to each other so as to seal a space surrounded by the respective inner peripheral edges. 
 
     
     
       4. The force sensor according to  claim 1 , wherein the center of each of the piezoresistance elements is positioned within ±10 μm from a corresponding portion of the inner peripheral edge of the sensor-side support. 
     
     
       5. The force sensor according to  claim 1 , further comprising:
 a package to which the base substrate is secured by adhesion, the package including:
 a plurality of electrode pads electrically connected to the plurality of electrode pads of the base substrate by wire bonding, and 
 a plurality of terminals for external connection, electrically connected to the plurality of electrode pads of the package; and 
 
 sealing resin that secures the respective peripheries of the base substrate and the sensor substrate on the package. 
 
     
     
       6. A force sensor having a sensor substrate joined to a base substrate,
 wherein the sensor substrate comprises:
 a pressure receiving unit formed on a first surface of the sensor substrate; 
 a displacement portion configured to be displaced by an external load applied thereto through the pressure receiving unit; 
 a plurality of piezoresistance elements provided on a second surface of the sensor substrate opposite to the first surface, each of the plurality of piezoresistance elements having an electrical resistance that changes in accordance with an amount of displacement of the displacement portion; 
 a sensor-side support provided on the second surface of the sensor substrate, configured to displaceable support the displacement portion, the sensor-side support being formed in a shape having an inner peripheral edge enclosing an entire periphery of the displacement portion in plan view, at least part of the sensor-side support overlapping the plurality of piezoresistance elements in plan view; and 
 a plurality of sensor-side electrically connecting portions provided on the second surface along a periphery of the sensor substrate so as to surround an outer periphery of the sensor-side support, each of the plurality of sensor-side electrically connecting portions being electrically connected to a corresponding one of the plurality of piezoresistance elements, and located at a separated position that does not cross a virtual line passing through a center of the pressure receiving unit and a center of each of the plurality of piezoresistance elements, 
 
 wherein the base substrate includes:
 a base-side support provided on a surface facing the sensor substrate, the base-side support being joined to the sensor-side support; 
 a plurality of base-side electrically connecting portions provided on the surface along a periphery of the base substrate so as to surround an outer periphery of the base-side support, the plurality of base-side electrically connecting portions being connected to the plurality of sensor-side electrically connecting portions; and 
 a plurality of electrode pads formed at ends of electrical wiring extending from the base-side electrically connecting portions, the plurality of electrode pads providing electrical connections to external circuitry, 
 
 wherein each of the plurality of sensor-side electrically connecting portions is disposed at a corresponding one of corners of the sensor substrate having a rectangular shape in plan view, and 
 wherein the sensor-side support is symmetrical with respect to a center of the displacement portion in plan view. 
 
     
     
       7. The force sensor according to  claim 6 ,
 wherein the sensor-side support has an outer periphery formed along the periphery of the sensor substrate except for the corners of the sensor substrate in plan view. 
 
     
     
       8. The force sensor according to  claim 6 ,
 wherein the sensor-side support also serves as one of the plurality of sensor-side electrically connecting portions. 
 
     
     
       9. The force sensor according to  claim 6 ,
 wherein the base-side support has a shape having an inner peripheral edge corresponding to the inner peripheral edge of the sensor-side support in plan view, the sensor-side support and the base-side support being joined to each other so as to seal a space surrounded by the respective inner peripheral edges. 
 
     
     
       10. The force sensor according to  claim 6 ,
 wherein the center of each of the piezoresistance elements is positioned within ±10 μm from a corresponding portion of the inner peripheral edge of the sensor-side support. 
 
     
     
       11. The force sensor according to  claim 6 , further comprising:
 a package to which the base substrate is secured by adhesion, the package including:
 a plurality of electrode pads electrically connected to the plurality of electrode pads of the base substrate by wire bonding, and 
 a plurality of terminals for external connection electrically connected to the plurality of electrode pads of the package; and 
 
 sealing resin that secures the respective peripheries of the base substrate and the sensor substrate on the package. 
 
     
     
       12. A method of manufacturing a force sensor, the method comprising:
 forming a plurality of sensor structures on one of front and rear panel surfaces of a sensor substrate panel having displacement portions, each of the plurality of sensor structures being formed for respective one of the plurality of displacement portions, each of the plurality of sensor structures including:
 a plurality of piezoresistance elements, each having an electrical resistance which changes in accordance with an amount of displacement of the displacement portion that is displaced, 
 a sensor-side support formed in a shape having an inner peripheral edge enclosing an entire periphery of the displacement portion in plan view, at least part of the sensor-side support overlapping the plurality of piezoresistance elements in plan view, the sensor-side support displaceably supporting the displacement portion; and 
 a plurality of sensor-side electrically connecting portions provided along a periphery of the sensor structure so as to surround an outer periphery of the sensor-side support, each of the plurality of sensor-side electrically connecting portions being electrically connected to a corresponding one of the plurality of piezoresistance elements and located at a separated position that does not cross a virtual line passing through a center of the pressure receiving unit and a center of each of the plurality of piezoresistance elements; 
 
 forming a plurality of base structures on one of front and rear panel surfaces of a base substrate panel, each of the plurality of base structures including:
 a plurality of base-side electrically connecting portions provided in positions corresponding to the plurality of sensor-side electrically connecting portions; 
 a plurality of electrode pads formed at ends of electrical wiring extending from the base-side electrically connecting portions so as to be wire-bondable, and 
 a base-side support provided in an area surrounded by the plurality of base-side electrically connecting portions so as to correspond to the sensor-side support; 
 
 joining the sensor substrate panel and the base substrate panel to each other by pressing the sensor substrate panel and the base substrate panel against each other and simultaneously joining the plurality of sensor-side electrically connecting portions to the corresponding base-side electrically connecting portions and the sensor-side supports to the corresponding base-side supports in an atmosphere in which the temperature is in a range from room temperature to a temperature lower than 250° C.; 
 forming a plurality of pressure receiving units on the other of the front and rear panel surfaces of the sensor substrate panel, an external load to be applied to a displacement portion of each sensor structure through a corresponding one of the pressure receiving units; and 
 cutting the sensor substrate panel and the base substrate panel into chips each including a pair of the sensor structure and the base structure. 
 
     
     
       13. The method of manufacturing the force sensor according to  claim 12 ,
 wherein each of the plurality of sensor-side electrically connecting portions, each of the plurality of base-side electrically connecting portions, each of the sensor-side supports, and each of the base-side supports have respective metal joint layers formed thereon, each metal joint layer having a thickness of 300 nm or smaller and being formed of an alloy including one or more of materials selected from the group consisting of Al, Ti, Cr, Ni, Cu, Ru, Rh, Ir, Pt, Ta, Fe, and Au, or a multilayer film composed of two or more layers each including a material selected from the group consisting of Al, Ti, Cr, Ni, Cu, Ru, Rh, Ir, Pt, Ta, Fe, and Au, and 
 wherein each of the plurality of sensor-side electrically connecting portions is joined to a corresponding one of the plurality of base-side electrically connecting portions with the metal joint layers interposed therebetween, and each of the sensor-side supports is joined to a corresponding one of the base-side supports with the metal joint layers interposed therebetween.